In the past, since a polypropylene-based resin is excellent in mechanical nature, chemical resistance, and the like, it has been utilized as a raw material of a variety of molded articles.
A molded article constituted of the polypropylene-based resin is generally prepared by extrusion molding, blow molding, expanding molding, or the like.
Since the polypropylene-based resin has generally crystallinity, the viscosity and melt tension at melting thereof are low.
For this reason, particularly when one tries to obtain an expanded molded article or the like constituted of the polypropylene-based resin, there is a problem that it is difficult to obtain an expanded sheet having a low open cell ratio.
In order to solve such a problem, adjustment of the melt properties by modifying the polypropylene-based resin with an aromatic vinyl monomer such as a styrene monomer has been studied.
Meanwhile, when a strain amount to be added to a polymer in the molten state per unit time is increased to measure the elongation viscosity, in general polymers, an approximately linear relationship is shown between a value of the strain amount and a value of the elongation viscosity.
On the other hand, specific polymers show nature that the elongation viscosity is rapidly increased from a certain strain amount.
Such nature is named as “strain hardening property” or the like.
The following Patent Document 1 describes a method of obtaining a modified polypropylene-based resin having “strain hardening property”.
In this Patent Document 1, in Examples or the like, there is described that, by reacting 10 parts by mass or more of a styrene monomer with 100 parts by mass of a polypropylene-based resin, strain hardening property which was not exerted only by a reaction of 2 parts by mass of a styrene monomer is exerted, and a rod-shaped foam is obtained in the good expanded state.